Fire, time-temperature profile

Fig. 2. Time—temperature profile for kettle calcination. Points A—B represent the fill period B—C, the boil or drag C—D, falling rate or cook-off D, discharge for hemihydrate. Points D—E show firing rate to second boil E—F, second boil F—G, second cook-off G, second-settle discharge.

Plots of time and temperature provide a basis for assessing fire severity. The procedure compares fires with different temperature histories to standard time-temperature profiles. A test fire is equivalent in severity to the standard when the areas under the time-temperature curves are equal. Barriers, such as walls, floors, ceilings, and doors, must be able to withstand the desired fire severity. 

Figure 7.3 Time-temperature profile of large scale fires [121] (Reproduced with permission from RJ. Far dell. Toxicity of Plastics and Rubber in Fire, Rapra Review Report No,69, Rapra Technology Ltd, 1993)...

Each time the photolysis laser fires a complete profile of the OH decay is obtained and recorded. A number of such decays are stored and averaged to reduce the signal to noise and bimolecular rate coefficients are obtained at a number of different temperatures by the procedures outlined above. 

AlO. Conventionally, excess air has been used to reduce temperature differences along the gas flow paths, but that approach costs more fuel. With pulsed flows, high mass flows accomplish the same more-level temperature profile as excess air but without the fuel cost and without the necessary added soak time. Stepped pulse firing allows soak times between its pulses. 

Belt furnaces having independently controlled heated zones through which a belt travels at a constant speed are commonly used for firing thick films. By adjusting the zone temperature and the belt speed, a variety of time vs. temperature profiles can be achieved. The furnace must also have provisions for atmosphere control during the firing process to prevent reduction (or, in the case of copper, oxidation) of the constituents. 

In the past, the use of scale models was not used because of the difficulties of establishing a relationship of heat flow between the two models, and the inability to achieve similarities in the temperature profiles. Some authors examined not only the potential of using small but simple analysis techniques to rate, calculated and established the structural requirements models. Using a normalized fire curve and the laws change over time scales to generate a similar temperatures profile in the model and in the test prototype were verified by experimental tests [ 16]. 

Numerical model calculations using the CFD code FLUENT 6.1 were performed to evaluate the time dependent behavior of fires ignited within a homogeneous porous canopy. These were compared with flow behavior from a similar fire in the absence of the canopy. Consideration was given to the effects of grid resolution, turbulence model (/c-RANS versus LES), wind speed (Uh = 0, 1, 2, 5 m/s), fire intensity (Q = 20, 50, 100 kW/m3), and inlet velocity profile (a = 0 or 0.14). The development of velocities, turbulence intensity, static pressure, and temperature fields were examined for such examples. Typical results are discussed below. 

Figure 17.1 Temperature/time fire profile (a) Fire development phase (b) Fully developed fire (c) Receding fire. Source Author s own files)...

Fire endurance models These models focus specifically on the mechanical cndmance of structures during fire, and so are generally finite element models which calculate changes in stress in response to temperature change within particular structural components of different materials, namely steels, masonries or polymer composites. They can be written in isolation or combined with either zone or field models to produce a comprehensive description of the fire scenario in terms of heat and mass flows as well as component stresses. Thus, such models can be used to predict the moment of struetural failure in a member with variable accuracy. One important specific result of such models is a temperature-time profile through the thickness of a structural component such as an I-beam for example. 

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